1. Field of the Invention
The present invention relates to a high-voltage variable resistor for regulating a focus voltage or a screen voltage of a TV receiver or other suitable device.
2. Description of the Related Art
A known high-voltage variable resistor for regulating a focus voltage or a screen voltage of a TV receiver is disclosed, for example, on pages 5 and 6 and in FIG. 1 of Japanese Unexamined Utility Model Registration Application Publication No. 6-2610. Such a high-voltage variable resistor includes a high-voltage variable-resistor substrate having a resistor element and land electrodes provided thereon. The front and rear sides of the base of the high-voltage variable-resistor substrate are electrically connected via through-holes provided at corresponding land electrodes, although this method is not specifically disclosed.
Referring now to FIG. 6, an undisclosed high-voltage variable-resistor substrate will be described. FIG. 6 is a plan view of a known high-voltage variable-resistor substrate 51.
The high-voltage variable-resistor substrate 51 includes a base 52 having a resistor element 61 and two land electrodes 62 and 63 on the front side thereof. The two land electrodes 62 and 63 include through-holes 64 and 65, respectively, in which a conductive paste or other suitable material is filled so as to electrically connect the front and rear sides of the base 52 of the high-voltage variable-resistor substrate 51. However, in the high-voltage variable-resistor substrate 51 used in the above-described known high-voltage variable resistor, the through-holes 64 and 65 are often insufficiently filled with the conductive paste or other suitable material depending upon the variations in printing conditions of the land electrodes, causing faulty electrical continuity between the front and rear sides of the base 52 of the high-voltage variable-resistor substrate 51, and accordingly, reducing the reliability of the high-voltage variable resistor.
Also, another known high-voltage variable resistor having an insulating case formed by fitting first and second insulating cases together is disclosed, for example, in Japanese Patent Application Publication No. 10-74605. The disclosed high-voltage variable resistor includes the insulating case, an insulating substrate provided in the insulating case and having a variable-resistor circuit pattern on the front surface thereof, and a slider arranged between the front surface of the insulating substrate and the insulating case.
The first and second insulating cases of the known high-voltage variable resistor are engaged with each other in the following manner. As shown in FIG. 7A, a front case 100a defining the first insulating case includes a side wall 122 at each peripheral side thereof. The side wall 122 includes two flat plate members 121 and a fitting depression 120 provided between the two flat plate members 121. The side wall 122 also includes an engaging hole 140 provided therein. One end of the engaging hole 140 is open at the inner wall of the fitting depression 120 and the other end is open at the outer wall of the front case 100a. 
Also, as shown in FIG. 7B, a rear case 100b defining the second insulating case includes a side wall 110 defined by a single flat plate member at each peripheral side thereof. The front of the side wall 110 is fitted into the fitting depression 120 of the front case 100a. In addition, the side walls 110 include an opening end 111 in which an engaging projection 130 is provided, and the engaging projection 130 elastically engages the engaging hole 140. More specifically, as shown in FIG. 7C, since the engaging projection 130 and the engaging hole 140 elastically engage each other, the front case 100a and the rear case 100b are attached together, thereby allowing the insulating case 100 to be formed without using a welding technique. Although only one side wall of the insulating case is illustrated in FIGS. 7A to 7C, the other three side walls are formed in substantially the same manner as described above.
The insulating substrate provided in the insulating case 100 includes a slit at each corner thereof, formed by cutting the insulating substrate from the peripheral side surface towards an inner portion thereof. The slits include elastic conductors, such as coil springs or conductive rubbers, fitted therein so as to sandwich the insulating substrate. The conductors are electrically connected to an input-terminal electrode and a ground terminal electrode provided on the front surface of the insulating substrate. Also, the conductors are electrically connected to input terminals and ground terminals inserted from the rear surface of the insulating substrate of the insulating case. As described above, the conductors define electrical conducting members between the input terminals and the ground terminals and the input-terminal and ground-terminal electrodes, respectively. In addition, when the insulating case is formed by fitting, the conductors are pressed by the inner bottom surfaces of the front and rear cases 100a and 100b such that the insulating substrate is sandwiched and held by this pressing force in the depth direction thereof.
However, in the known high-voltage variable resistor, since the engaging projection 130 of the rear case 100b is provided in the opening end 111 of the side walls 110, and also one end of the engaging hole 140 of the front case 100a is open at the inner wall of the fitting depression 120 and the other end is open at the outer wall of the front case 100a, the insulating case 100 has a gap 150, in communication with the inside thereof, provided at the engaging portion between the engaging projection 130 and the engaging hole 140. Accordingly, there is a risk that dust, moisture, or other impurities will intrude into the inside of the insulating case 100 of the variable resistor through the gap 150, and a poor connection or deteriorated characteristics may occur. Also, the gap 150 greatly reduces the dielectric strength of the variable resistor.
In addition, the known high-voltage variable resistor has a problem in that not only does fitting the conductors in the slits provided in the insulating substrate require an additional manufacturing step, but also the slits reduce the durability of the insulating substrate and increase the defective ratio of products through breakage.
In order to overcome the above-described problems, preferred embodiments of the present invention provide a high-voltage variable resistor including front and rear cases defining an insulating case that are reliably brought into close contact and engaged with each other without producing a gap at any engaging portions in the side walls of the front and rear cases, an insulating substrate is fixed in the insulating case without forming a slit therein, and also input terminals and ground terminals are electrically connected with corresponding terminal electrodes on the front surface of the insulating substrate.
A high-voltage variable resistor according to preferred embodiments of the present invention includes an insulating case, having first and second insulating cases, and a high-voltage variable-resistor substrate. The high-voltage variable-resistor substrate includes a base having a resistor element on the front surface thereof, a plurality of through-hole electrodes arranged so as to extend through the base, and at least one land electrode provided on each of the front and rear surfaces of the base and connected to the through-hole electrodes. The plurality of the through-hole electrodes is provided at the land electrode of the high-voltage variable-resistor substrate, the high-voltage variable-resistor substrate is housed in the insulating case, at least one conductor is disposed in the second insulating case, and the conductor and the land electrode on the rear surface of the high-voltage variable-resistor substrate are electrically connected to each other.
In the high-voltage variable resistor according to preferred embodiments of the present invention, the plurality of through-hole electrodes are arranged around the at least one land electrode along an approximate circle.
In the high-voltage variable resistor according to preferred embodiments of the present invention, each portion of the land electrode surrounding a corresponding one of the plurality of through-hole electrodes, preferably has substantially the same shape.
With this arrangement, since each land electrode includes the plurality of through-hole electrodes provided thereat, even when one of the through-hole electrodes has faulty electrical continuity, the front and rear surfaces of the base of the high-voltage variable-resistor substrate are electrically connected with each other via the other through-hole electrodes, thereby greatly reducing the defective ratio and greatly increasing the reliability of the high-voltage variable resistor.
Also, since the plurality of through-holes are arranged along an approximate circle, stresses in the base produced when the through-holes are formed by punching are evenly decentralized, thereby greatly reducing the probability of breakage of the base, and thus, greatly increasing the reliability of the high-voltage variable resistor.
In addition, since portions of the plurality of land electrodes have substantially the same shape, when the through-holes are to be filled with a conductor such as a conductive paste, the conductor is more evenly filled in all the through-holes, thereby reducing the required amount of filling conductor, and thus, increasing the productivity of the high-voltage variable resistors.
The high-voltage variable resistor according to preferred embodiments of the present invention preferably further include at least one rotating shaft including a slider which slides on the resistor element. The first insulating case includes a plate-like portion, side walls provided along the peripheral sides of the plate-like portion, at least one bearing which is disposed in the plate-like portion and which rotatably supports the rotating shaft, an opening end defined by the side walls, and at least one first engaging member arranged at a predetermined location of the side walls. Also, the second insulating case includes a plate-like portion, side walls disposed along the peripheral sides of the plate-like portion, an opening end defined by the side walls, and at least one second engaging member arranged at a predetermined location of the side walls. In addition, by engaging the first engaging member of the side walls of the first insulating case with the second engaging member of the side walls of the second insulating case, the high-voltage variable-resistor substrate is housed in the insulating case, and the first insulating case and the second insulating case are engaged with each other so as not to produce a gap therebetween which extends to the inside of the insulating case.
More particularly, in the high-voltage variable resistor according to preferred embodiments of the present invention, the engaging member disposed at the predetermined places of the side walls of the first and second insulating cases are preferably provided at the location other than the opening ends. For example, one of the engaging members disposed at the predetermined locations of the side walls of the first and second insulating cases is an engaging projection, and the other is one of an engaging groove, an engaging depression, and an engaging step.
In the high-voltage variable resistor according to preferred embodiments of the present invention, either of each side wall of the first insulating case and each side wall of the second insulating case preferably includes at least one flat plate member, and the other preferably includes a plurality of flat plate members and includes at least one depression between the flat plate members. The side wall defined by the at least one flat plate member is inserted into the depression. Also, the engaging members include the engaging projection, disposed at the side wall defined by said at least one flat plate member, and one of the engaging groove, the engaging depression, and the engaging step disposed at the outermost plate member of the side wall defined by the plurality of flat plate members. In addition, the engaging projection is engaged with one of the engaging groove, the engaging depression, and the engaging step.
With the above-described arrangement, since the engaging members are disposed at the predetermined locations of the side walls of the first and second insulating cases, and the first and second insulating cases are engaged with each other so as to prevent a gap in communication with the inside of the insulating case from being produced, the inside of the insulating case is completely covered by the first and the second insulating cases. Accordingly, there is no risk of an undesirable substance intruding into the insulating case, thereby preventing occurrence of a poor connection or characteristic deterioration, and also increasing a dielectric strength since no gap is produced.
In the high-voltage variable resistor according to preferred embodiments of the present invention, either of the side walls of the first and second insulating cases preferably includes depressions on the inner walls thereof, and the high-voltage variable-resistor substrate is preferably held and fixed in the insulating case by inserting the substrate into the depressions. With this structure, the substrate is held and fixed in the insulating case without requiring a slit to be formed in the substrate.
Furthermore, the land electrodes are provided on the rear surface of the high-voltage variable-resistor substrate and are electrically connected to those provided on the front surface of the high-voltage variable-resistor substrate via the through-hole electrodes, at least two elastic conductors are disposed in the plate-like portion of the second insulating case, and the conductors and the land electrodes provided on the rear surface of the high-voltage variable-resistor substrate are brought into press-contact with each other so as to be electrically connected. This structure allows the high-voltage variable-resistor substrate to be clamped by the conductors, the high-voltage variable-resistor substrate to be fixed in the insulating case, and the input and ground terminals inserted into the conductors provided on the rear surface of the high-voltage variable-resistor substrate to be electrically connected to the land electrodes on the front surface of the high-voltage variable-resistor substrate. The conductors are preferably made of a conductive material such as a conductive rubber. With this arrangement, the input and ground terminals are easily inserted into the conductors and the high-voltage variable resistor is easily assembled.